In hierarchical cache management system, only a subset of data in the higher level caches (caches further away from the processor) are available in the lower level caches (caches closer to the processor). Every time a new cache line is being copied over from a higher level cache to a lower level cache, an existing cache line in the lower level cache needs to be replaced with the new cache line. In a set associative cache structure, there are multiple choices for the cache line to be evicted, for every incoming cache line. How the eviction address is selected is called the replacement policy.